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Frequency Domain Noise Shaping To unify processing of AAC and TCX frames, the MDCT transform in TCX is applied in the original signal domain Noise shaping for TCX frames is performed in the MDCT domain based on LPC filters mapped to the MDCT domain FDNS allows a smooth (sample-by-sample) time- domain noise envelope by applying a 1st-order filtering to the MDCT coefficients (similar in principle to TNS)

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Effect of FDNS on the spectral shape and the time-domain envelope of the noise time axis (n) A B C Noise gains g 1 [m] calculated at time position A Interpolated gains seen in the time domain, for each of the M bands Noise gains g 2 [m] calculated at time position B Frequency axis (k or m) Frequency axis (k or m)

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Forward Aliasing Cancellation FAC is applied in the original signal domain FAC is quantized in the LPC weighted domain so that quantization noises of FAC and decoded MDCT are of the same nature For transition from ACELP to TCX, the ACELP synthesis can be taken into account; this reduces the bitrate needed to encode FAC

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Computation of FAC targets for transitions from and to ACELP (encoder)